Covering grid plates for ventilation openings

ABSTRACT

The use of a thermoplastic molding composition differing from ABS and comprising, based on a total of 100% by weight of amounts of components A and B, and, if desired, C and/or D, 
     a: as component A, from 1 to 99% by weight, preferably from 15 to 60% by weight, in particular from 25 to 50% by weight, of a particulate emulsion polymer with a glass transition temperature of below 0° C. and with a median particle size of from 50 to 1000 nm, preferably from 50 to 500 nm, 
     b: as component B, from 1 to 99% by weight, preferably from 40 to 85% by weight, in particular from 50 to 75% by weight, of at least one amorphous or partly crystalline polymer, 
     c: as component C, from 0 to 50% by weight of polycarbonates, and 
     d: as component D, from 0 to 50% by weight of fibrous or particulate fillers or mixtures of these 
     for producing covering grid plates for ventilator openings.

The invention relates to covering grid plates for ventilator openings.The invention relates in particular to covering grid plates with highweathering resistance together with yellowing resistance, high surfacequality and low tendency to develop weld lines.

Various materials have hitherto been used for producing ventilator gridsor ventilator gratings. Use has been made, for example, of steel plate,but this offers only limited possibilities for shaping. In addition,steel plate is susceptible to corrosion and tends to create noise(rattle) when a ventilator is operating.

ABS (acrylonitrile/butadiene/styrene copolymer) and HIPS (high-impactpolystyrene) are also used. Yellowing resistance is not adequate forevery application. Yellowing is associated with a fall-off in thetoughness of the material, and also with a roughening of the surface.Long exposures to heat cause a fall-off in strength, and in manyinstances therefore mechanical strength becomes inadequate if suchexposure is prolonged.

Another material used is PVC (polyvinyl chloride). As well as thedisadvantages resulting from its chlorine content, PVC is difficult toinjection mold. In addition, PVC has low heat resistance.

It is an object of the present invention to provide covering grid platesfor ventilator openings which have high yellowing resistance and highweathering resistance. Another object of the present invention is toprovide covering grid plates for ventilator openings which, in theirmanufacture, have little tendency to develop weld lines, and also havehigh surface quality. A further object of the invention is to providecovering grid plates for ventilator openings which avoid thedisadvantages of the known covering grid plates.

We have found that this object is achieved by using a moldingcomposition which differs from ABS and comprises, based on the total ofthe amounts of components A and B, and, if desired, C and/or D, which is100% by weight in total,

a: as component A, from 1 to 99% by weight of a particulate emulsionpolymer with a glass transition temperature of below 0° C. and with amedian particle size of from 50 to 1000 nm,

b: as component B, from 1 to 99% by weight of at least one amorphous orpartly crystalline polymer,

c: as component C, from 0 to 50% by weight of polycarbonates, and

d: as component D, from 0 to 50% by weight of fibrous or particulatefillers or mixtures of these

for producing covering grid plates for ventilator openings.

The thermoplastic molding compositions used according to the inventionfor producing the novel covering grid plates are known per se. Moldingcompositions which can be used according to the invention are described,for example, in DE-A-12 60 135, DE-C-19 11 882, DE-A-28 26 925, DE-A-3149 358, DE-A-32 27 555 and DE-A-40 11 162.

In one embodiment, the molding compositions differing from ABS and usedaccording to the invention for producing the novel covering grid platescomprise the components listed below: A and B, and, if desired, C and/orD, as defined further below. Based on a total of 100% by weight ofamounts of components A and B, and, if desired, C and/or D, theycomprise

a: as component A, from 1 to 99% by weight, preferably from 15 to 60% byweight, in particular from 25 to 50% by weight, of a particulateemulsion polymer with a glass transition temperature of below 0° C. andwith a median particle size of from 50 to 1000 nm, preferably from 50 to55 nm,

b: as component B, from 1 to 99% by weight, preferably from 40 to 85% byweight, in particular from 50 to 75% by weight, of at least oneamorphous or partly crystalline polymer,

c: as component C, from 0 to 50% by weight of polycarbonates, and

d: as component D, from 0 to 50% by weight of fibrous or particulatefillers or mixtures of these.

The invention is described in more detail below.

The molding compositions used for producing the novel covering gridplates are firstly described together with the components of which thesecompositions are composed.

COMPONENT A

Component A is a particulate emulsion polymer with a glass transitiontemperature of below 0° C. and with a median particle size of from 50 to1000 nm.

Component A is preferably a graft copolymer made from

a1: from 1 to 99% by weight, preferably from 55 to 80% by weight, inparticular from 55 to 65% by weight, of a particulate graft base A1 witha glass transition temperature of below 0° C.,

a2: from 1 to 99% by weight, preferably from 20 to 45% by weight, inparticular from 35 to 45% by weight, of a graft A2 made from themonomers, based on A2, a21: as component A21, from 40 to 100% by weight,preferably from 65 to 85% by weight, of units of a vinylaromaticmonomer, preferably of styrene, of a substituted styrene or of a(meth)acrylate or mixtures of these, in particular of styrene and/or ofα-methylstyrene, and

a22: as component A22, up to 60% by weight, preferably from 15 to 35% byweight, of units of an ethylenically unsaturated monomer, preferably ofacrylonitrile or methacrylonitrile, in particular of acrylonitrile.

The graft A2 here is composed of at least one graft shell, and theoverall graft copolymer A has a median particle size of from 50 to 1000nm.

In one embodiment of the invention, component A1 is composed of thefollowing monomers:

a11: as component A11, from 80 to 99.99% by weight, preferably from 95to 99.9% by weight, of a C₁ -C₈ -alkyl acrylate, preferably n-butylacrylate and/or ethylhexyl acrylate, and

a12: as component A12, from 0.01 to 20% by weight, preferably from 0.1to 5.0% by weight, of at least one polyfunctional crosslinking monomer,preferably diallyl phthalate and/or DCPA.

In one embodiment of the invention the median particle size of componentA is from 50 to 800 nm, preferably from 50 to 600 nm.

In another embodiment of the invention, the particle size distributionof component A is bimodal, where, based on the total weight of componentA, from 60 to 90% by weight has a median particle size of from 50 to 200nm and from 10 to 40% by weight has a median particle size of from 50 to400 nm.

The median particle size and particle size distribution given are thesizes determined from the integral mass distribution. The medianparticle sizes according to the invention are in all cases the weightaverage of the particle sizes. The determination of these is based onthe method of W. Scholtan and H. Lange, Kolloid-Z. and Z.-Polymere 250(1972), pages 782-796, using an analytical ultracentrifuge. Theultracentrifuge measurement gives the integral mass distribution of theparticle diameter of a specimen. From this it is possible to deduce whatpercentage by weight of the particles have a diameter identical to orsmaller than a particular size. The median particle diameter, which isalso termed the d₅₀ of the integral mass distribution, is defined hereas the particle diameter at which 50% by weight of the particles have adiameter smaller than that corresponding to the d₅₀. Equally, 50% byweight of the particles then have a larger diameter than the d₅₀. Todescribe the breadth of the particle size distribution of the rubberparticles, d₁₀ and d₉₀ values given by the integral mass distributionare utilized alongside the d₅₀ value (median particle diameter). The d₁₀and d₉₀ of the integral mass distribution are defined similarly to thed₅₀ with the difference that they are based on, respectively, 10 and 90%by weight of the particles. The quotient ##EQU1## is a measure of thebreadth of the particle size distribution. Emulsion polymers A which canbe used according to the invention as component A preferably have Q lessthan 0.5, in particular less than 0.35.

The glass transition temperature of the emulsion polymer A, and also ofthe other components used according to the invention, is determinedusing DSC (differential scanning calorimetry) in accordance with ASTM3418 (midpoint temperature).

The rubbers which can be used as emulsion polymer A are the usualrelevant rubbers such as, in one embodiment of the invention,epichlorohydrin rubbers, ethylene-vinyl acetate rubbers, polyethylenechlorosulfone rubbers, silicone rubbers, polyether rubbers, hydrogenateddiene rubbers, polyalkenamer rubbers, acrylate rubbers,ethylene-propylene rubbers, ethylene-propylene-diene rubbers, butylrubbers and fluorine rubbers. Preference is given to acrylate rubber,ethylene-propylene (EP) rubber and ethylene-propylene-diene (EPDM)rubber, in particular acrylate rubber.

Pure butadiene rubbers, as used in ABS, may not be used as the solecomponent A.

In one embodiment, the fraction of the fundamental diene building blockin the emulsion polymer A is held so low that very few unreacted doublebonds remain in the polymer. In one embodiment there are no fundamentaldiene building blocks in the emulsion polymer A.

The acrylate rubbers are preferably alkyl acrylate rubbers made from oneor more C₁ -C₈ -alkyl acrylates, preferably C₄ -C₈ -alkyl acrylates,where use is preferably made at least to some extent of butyl, hexyl,octyl or 2-ethylhexyl acrylate, in particular n-butyl and 2-ethylhexylacrylate. These alkyl acrylate rubbers may comprise as comonomers up to30% by weight of monomers which form hard polymers, for example vinylacetate, (meth)acrylonitrile, styrene, substituted styrene, methylmethacrylate or vinyl ethers.

In one embodiment of the invention the acrylate rubbers further comprisefrom 0.01 to 20% by weight, preferably from 0.1 to 5% by weight, ofpolyfunctional monomers with crosslinking action (crosslinkingmonomers). Examples of these are monomers which contain 2 or more doublebonds capable of copolymerization, preferably not conjugated in 1,3positions.

Examples of suitable crosslinking monomers are divinylbenzene, diallylmaleate, diallyl fumarate, diallyl phthalate, diethyl phthalate,triallyl cyanurate, triallyl isocyanurate, ricyclodecenyl acrylate,dihydrodicyclopentadienyl acrylate, triallyl phosphate, allyl crylateand allyl methacrylate. Dicyclopentadienyl acrylate (DCPA) has proven tobe a particularly useful crosslinking monomer (cf DE-C 12 60 135).

Examples of suitable silicone rubbers are crosslinked silicone rubbersmade from units of the general formulae R₂ SiO, RSiO_(3/2), R3SiO_(1/2)and SiO_(2/4), where R is a monovalent radical. The amounts of theindividual siloxane units here are judged in such a way that for each100 units of the formula R₂ SiO there are from 0 to 10 molar units ofthe formula RSiO3/2, from 0 to 1.5 molar units of R3SiO_(1/2) and from 0to 3 molar units of SiO_(2/4). R here can be either a monovalentsaturated hydrocarbon radical having from 1 to 18 carbon atoms, phenylor alkoxy or a group susceptible to free-radical attack, for examplevinyl or mercaptopropyl. At least 80% of the radicals R are preferablymethyl radicals. Combinations of methyl and ethyl or phenyl radicals areparticularly preferred.

Preferred silicone rubbers incorporate units of groups susceptible tofree-radical attack, in particular vinyl, allyl, halo or mercaptogroups, preferably in amounts of from 2 to 10 mol % based on all of theradicals R. They may, for example, be prepared as described in EP-A-0260 558.

It can be useful in some cases to use an emulsion polymer A made fromuncrosslinked polymer. Monomers which can be used to prepare thesepolymers are all of the abovementioned monomers. Examples of preferreduncrosslinked emulsion polymers A are homo- and copolymers of acrylates,in particular of n-butyl and of ethylhexyl acrylate, and also homo- andcopolymers of ethylene, of propylene, of butylene, of isobutylene, andalso poly(organosiloxanes). In all cases these may be linear or elsebranched.

Core-shell Emulsion Polymer A

Emulsion polymer A can also be a polymer built up in more than one stage(have core-shell morphology). For example, an elastomeric core (Tg<0°C.) may have been encapsulated by a hard shell (polymers with Tg>0° C.)or vice versa.

In a particularly preferred embodiment of the invention, component A isa graft copolymer. The graft copolymers A of the molding compositionsaccording to the invention here have a median particle size d₅₀ of from50 to 1000 nm, preferably from 50 to 600 nm, and particularly preferablyfrom 50 to 400 nm. These particle sizes may be achieved if particlesizes of from 50 to 350 nm, preferably from 50 to 300 nm andparticularly preferably from 50 to 250 nm, are used as graft base A1 ofthis component A.

The graft copolymer A generally has one or more stages, i.e. is apolymer built up from a core and from one or more shells. The polymer iscomposed of a base (graft core) A1 and of one or preferably more thanone stage A2 (graft) grafted onto this, known as the graft stages orgraft shells.

One or more graft shells may be applied to the rubber particles viasimple grafting or multiple stepwise grafting. Each graft shell may havea different formulation. In addition to the grafting monomers andtogether with these, polyfunctional crosslinking monomers or monomerscontaining reactive groups may be grafted on (see, for example, EP-A-0230 282, DE-A-36 01 419 and EP-A-0 269 861).

In a preferred embodiment, component A is composed of a graft copolymerbuilt up in more than one stage, where the grafts have generally beenprepared from resin-forming monomers and have a glass transitiontemperature Tg above 30° C., preferably above 50° C. The structure withmore than one stage serves, inter alia, to achieve some degree ofcompatibility of the rubber particles A with the thermoplastic B.

Graft copolymers A are prepared, for example, by grafting at least oneof the monomers A2 listed below onto at least one of the graft bases (orgraft core materials) A1 listed above. Suitable graft bases A1 in themolding compositions according to the invention are any of the polymerswhich have been described above under the emulsion polymers A.

In one embodiment of the invention the graft base A1 has been formulatedfrom from 15 to 99% by weight of acrylate rubber, from 0.1 to 5% byweight of crosslinking agent and from 0 to 49.9% by weight of one of theother monomers or rubbers stated.

Suitable monomers for forming the graft A2 may, for example, have beenselected from the monomers listed below and mixtures of these:

vinylaromatic monomers, such as styrene and its substituted derivativessuch as α-methylstyrene, p-methylstyrene, 3,4-dimethylstyrene,p-tert-butylstyrene, o- and p-divinylbenzene andp-methyl-α-methylstyrene, and C₁ -C₈ -alkyl (meth)acrylates, such asmethyl methacrylate, ethyl methacrylate, methyl acrylate, ethylacrylate, n-butyl acrylate and sec-butyl acrylate. Preference is givento styrene, α-methylstyrene and methyl methacrylate, in particularstyrene and/or α-methylstyrene, and ethylenically unsaturated monomers,such as acrylic and methacrylic compounds, for example acrylonitrile,methacrylonitrile, acrylic and methacrylic acid, methyl acrylate, ethylacrylate, n-propyl and isopropyl acrylate, n-butyl and isobutylacrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, methylmethacrylate, ethyl methacrylate, n-propyl and isopropyl methacrylate,n-butyl and isobutyl methacrylate, tert-butyl methacrylate, cyclohexylmethacrylate, isobornyl methacrylate, and maleic anhydride and itsderivatives, such as maleic esters, maleic diesters and maleimides, e.g.alkyl- and arylmaleimides, for example methyl- and phenylmaleimide.Preference is given to acrylonitrile and methacrylonitrile, inparticular acrylonitrile.

Other (co)monomers which may be used are styrene compounds, vinylcompounds, acrylic or methacrylic compounds (e.g. styrene, substitutedif desired with C₁ -C₁₂ -alkyl radicals, with halogen or withhalomethylene radicals; vinylnaphthalene, vinylcarbazole; vinyl ethershaving C₁ -C₁₂ ether radicals; vinylirnidazole, 3-(4-)vinylpyridine,dimethylaminoethyl (meth)acrylate, p-dimethylaminostyrene,acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, butylacrylate, ethylhexyl acrylate and methyl methacrylate, and also fumaricacid, maleic acid or itaconic acid or their anhydrides, amides, nitrilesor esters with alcohols containing from 1 to 22 carbon atoms, preferablyfrom 1 to 10 carbon atoms).

In one embodiment of the invention component A encompasses from 50 to90% by weight of the graft base A1 described above and from 10 to 50% byweight of the graft A2 described above, based on the total weight ofcomponent A.

In one embodiment of the invention crosslinked acrylate polymers with aglass transition temperature below 0° C. are used as graft base A1. Thecrosslinked acrylate polymers should preferably have a glass transitiontemperature below -20° C., in particular below -30° C.

In a preferred embodiment the graft A2 is composed of at least one graftshell and the outermost graft shell of these has a glass transitiontemperature above 30° C., where a polymer formed from the monomers ofthe graft A2 would have a glass transition temperature above 80° C.

With respect to measurement of the glass transition temperature and themedian particle size, and also the values of Q, that which has been saidfor the emulsion polymers A is applicable to the graft copolymers A.

The graft copolymers A may also be prepared by grafting preformedpolymers onto suitable graft homopolymers. Examples of this are theproducts from reaction of base-containing rubbers with copolymerscontaining maleic anhydride groups or containing acid groups.

Suitable preparation processes for graft copolymers A are emulsion,solution, bulk and suspension polymerization. The graft copolymers A arepreferably prepared by free-radical emulsion polymerization, inparticular in the presence of latices of component A1 at temperatures offrom 20 to 90° C., using water-soluble or oil-soluble initiators, suchas peroxodisulfate or benzoyl peroxide, or with the aid of redoxinitiators. Redox initiators are also suitable for polymerization atbelow 20° C.

Suitable emulsion polymerization processes are described in DE-A-28 26925 and 31 49 358 and in DE-C-12 60 135.

The graft shells are preferably built up in an emulsion polymerizationprocess, as described in DE-A-32 27 555, 31 49 357, 31 49 358 and 34 14118. The specified setting of the particle sizes according to theinvention of from 50 to 1000 nm preferably takes place by the processesdescribed in DE-C-12 60 135 and DE-A-28 26 925, and Applied PolymerScience, Vol. 9 (1965), page 2929. The use of polymers with differentparticle sizes is known, for example, from DE-A-28 26 925 and U.S. Pat.No. 5,196,480.

According to the process described in DE-C-12 60 135, the graft base A1is first prepared by polymerizing the acrylate(s) used in one embodimentof the invention and the polyfunctional monomer which brings aboutcrosslinking, if desired together with the other comonomers, in aqueousemulsion in a manner known per se at temperatures of from 20 to 100° C.,preferably from 50 to 80° C. The usual emulsifiers may be used, such asalkali metal salts of alkyl- or alkylarylsulfonic acids, alkyl sulfates,fatty alcohol sulfonates, salts of higher fatty acids having from 10 to30 carbon atoms or resin soaps. Preference is given to the use of thesodium salts of alkylsulfonates or fatty acids having from 10 to 18carbon atoms. In one embodiment the amounts of the emulsifiers used arefrom 0.5 to 5% by weight, in particular from 1 to 2% by weight, based onthe monomers used in preparing the graft base A1. The weight ratio ofwater to monomers is generally from 2:1 to 0.7:1. The polymerizationinitiators used are in particular the common persulfates, such aspotassium persulfate. However, redox systems may also be used. Theinitiators are generally used in amounts of from 0.1 to 1% by weight,based on the monomers used in preparing the graft base A1. Otherpolymerization auxiliaries which may be used in the polymerization arethe usual buffer substances by means of which the pH can be set atpreferably from 6 to 9, for example sodium bicarbonate and sodiumpyrophosphate, and also from 0 to 3% by weight of a molecular weightregulator, such as mercaptans, terpinols or dimeric α-methylstyrene.

The precise polymerization conditions, in particular the type, method ofaddition and amount of the emulsifier, are individually determinedwithin the ranges given above in such a way that the d₅₀ of theresultant latex of the crosslinked acrylate polymer is in the range fromabout 50 to 1000 nm, preferably from 50 to 150 nm, particularlypreferably from 80 to 100 nm. The particle size distribution of thelatex here should preferably be narrow. The quotient ##EQU2## should be<0.5, preferably <0.35.

In a subsequent step, polymerization of a monomer mixture made fromstyrene and acrylonitrile in the presence of the resultant latex of thecrosslinked acrylate polymer in one embodiment of the invention iscarried out to prepare the graft polymer A, where in one embodiment ofthe invention the weight ratio of styrene to acrylonitrile in themonomer mixture should be in the range from 100:0 to 40:60, andpreferably from 65:35 to 85:15. This graft copolymerization of styreneand acrylonitrile onto the crosslinked polyacrylate polymer serving as agraft base is advantageously again carried out in aqueous emulsion underthe usual conditions described above. The graft copolymerization mayusefully take place in the system used for the emulsion polymerizationto prepare the graft base A1, where further emulsifier and initiator maybe added if necessary. The mixture of styrene and acrylonitrile monomerswhich is to be grafted on in one embodiment of the invention may beadded to the reaction mixture all at once, in portions in more than onestep, or preferably continuously during the course of thepolymerization. The graft copolymerization of the mixture of styrene andacrylonitrile in the presence of the crosslinking acrylate polymer iscarried out in such a way as to obtain in graft copolymer A a degree ofgrafting of from 1 to 99% by weight, preferably from 20 to 45% byweight, in particular from 35 to 45% by weight, based on the totalweight of component A. Since the grafting yield in the graftcopolymerization is not 100% the amount of the mixture of styrene andacrylonitrile monomers which has to be used in the graftcopolymerization is somewhat greater than that which corresponds to thedesired degree of grafting. Control of the grafting yield in the graftcopolymerization, and therefore of the degree of grafting of thefinished graft copolymer A, is a topic with which the person skilled inthe art is familiar. It may be achieved, for example, via the meteringrate of the monomers or via addition of regulator (Chauvel, Daniel, ACSPolymer Preprints 15 (1974), pp. 329 ff.). The emulsion graftcopolymerization generally gives from about 5 to 15% by weight, based onthe graft copolymer, of free, ungrafted styrene-acrylonitrile copolymer.The proportion of the graft copolymer A in the polymerization productobtained in the graft copolymerization is determined by the method givenabove.

Preparation of the graft copolymers A by the emulsion process gives,besides the technical process advantages stated above, the possibilityof reproducible changes in particle sizes, for example by agglomeratingthe particles at least to some extent to give larger particles. Thisimplies that polymers with different particle sizes may also be presentin the graft copolymers A.

In particular, component A made from graft base and graft shell(s) canbe matched ideally to the respective application, and in particular withrespect to particle size.

Graft copolymers A generally comprise from 1 to 99% by weight,preferably from 55 to 80 and particularly preferably from 55 to 65% byweight, of graft base A1 and from 1 to 99% by weight, preferably from 20to 45, particularly preferably from 35 to 45% by weight, of the graftA2, based in each case on the entire graft copolymer.

COMPONENT B

Component B is an amorphous or partly crystalline polymer.

Component B is preferably a copolymer made from

b1: as component B1, from 40 to 100% by weight, preferably from 60 to70% by weight, of units of a vinylaromatic monomer, preferably ofstyrene or of a substituted styrene or of a (meth)acrylate or mixturesof these, in particular of styrene and/or of α-methylstyrene, and

b2: as component B2, up to 60% by weight, preferably from 30 to 40% byweight, of units of an ethylenically unsaturated monomer, preferably ofacrylonitrile or of methacrylonitrile, in particular of acrylonitrile.

In a preferred embodiment of the invention, the viscosity number ofcomponent B is from 50 to 90, preferably from 60 to 80.

The amorphous or partly crystalline polymers of component B of themolding composition used according to the invention for producing thenovel covering grid plates are preferably at least one polymer selectedfrom the class consisting of partly crystalline polyamides, partiallyaromatic copolyamides, polyolefins, ionomers, polyesters, polyetherketones, polyoxyalkylenes, polyarylene sulfides and polymers made fromvinylaromatic monomers and/or ethylenically unsaturated monomers. It isalso possible to use polymer mixtures.

Polyamides suitable as component B of the molding composition usedaccording to the invention for producing the novel covering grid platesare partly crystalline, preferably linear polyarnides, such as nylon-6,nylon-6,6, nylon-4,6 and nylon-6,12, and partly crystalline copolyamidesbased on these components. It is also possible to use partly crystallinepolyamides whose acid component is composed partly or entirely of adipicacid and/or terephthalic acid and/or isophthalic acid and/or subericacid and/or sebacic acid and/or azelaic acid and/or dodecanedicarboxylicacid and/or of a cyclohexanedicarboxylic acid, and whose diaminecomponent is composed in particular partly or entirely of m- and/orp-xylylenediamine and/or hexamethylenediamine and/or 2,2,4- and/or2,4,4-trimethylhexamethylenediamine and/or isophoronediamine, and whoseformulations in principle are known from the prior art (cf. Encyclopediaof Polymers, Vol. 11, p. 315 ff).

Examples of other polymers suitable as component B of the moldingcompositions used according to the invention for producing the novelcovering grid plates are partly crystalline polyolefins, preferablyhomo- and copolymers of olefins such as ethylene, propylene, 1-butene,1-pentene, 1-hexene, 1-heptene, 3-methyl-1-butene, 4-methyl-1-butene,4-methyl-1-pentene and 1-octene. Suitable polyolefins are polyethylene,polypropylene, poly-1-butene and poly-4-methyl-1-pentene. Underpolyethylene (PE) a distinction is made in general between high-densityPE (HDPE), low-density PE (LDPE) and linear low-density PE (LLDPE).

In another embodiment of the invention ionomers are component B. Theseare generally polyolefins as described above, in particularpolyethylene, which comprise cocondensed monomers with acid groups, e.g.acrylic acid, methacrylic acid and, if desired, other copolymerizablemonomers. The acid groups are generally converted with the aid of metalions, such as Na⁺, Ca²⁺, Mg²⁺ and Al³⁺ into ionic, if desired ionicallycrosslinked, polyolefins which, however, can still be processedthermoplastically (see, for example, U.S. Pat. No. 3,264,272; 3,404,134;3,355,319 and 4,321,337). However, the essential to conversion of thepolyolefins containing acid groups by the use of metal ions is notessential. Polyolefins containing free acid groups are also suitable ascomponent B according to the invention. These then generally haverubbery character and to some extent comprise yet other copolymerizablemonomers, e.g. (meth)acrylates.

Besides these, polyesters, preferably aromatic/aliphatic polyesters, mayalso be used as component B. Examples of these are polyalkyleneterephthalates, e.g. based on ethylene glycol, 1,3-propanediol,1,4-butanediol, 1,6-hexanediol and 1,4-bis(hydroxymethyl)-cyclohexane,and also polyalkylene naphthalates.

Aromatic polyether ketones, for example as described in the publicationsGB 1 078 234, U.S. Pat. No. 4,010,147, EP-A-0 135 938, EP-A-0 292 211,EP-A-0 275 035, EP-A-0 270 998 and EP-A-0 165 406, and in thepublication by C. K. Sham et al., Polymer 29/6, (1988), 1016-1020, mayalso be used as component B.

Polyoxyalkylenes, e.g. polyoxymethylene, and oxymethylene polymers mayalso be used as component B of the molding compositions used accordingto the invention for producing the novel covering grid plates.

Other polymers suitable as component B are polyarylene sulfides, inparticular polyphenylene sulfide.

In one embodiment of the invention, the component is built up from from50 to 99% by is weight of vinylaromatic monomers and from from 1 to 50%by weight of at least one of the other monomers given.

Component B is preferably an amorphous polymer, as described above inthe form of graft A2. In one embodiment of the invention, component B isa copolymer of styrene and/or α-methylstyrene with acrylonitrile. Theacrylonitrile content in these copolymers of component B is from 0 to60% by weight, preferably from 30 to 40% by weight, based on the totalweight of component B. The free, non-grafted styrene-acrylonitrilecopolymers produced during the graft copolymerization to preparecomponent A also count as part of component B. Depending on theconditions selected for the graft copolymerization to prepare the graftcopolymer A, a sufficient proportion of component B may already havebeen formed during the graft copolymerization. However, it willgenerally be necessary for the products obtained in the graftcopolymerization to be blended with additional component B preparedseparately.

This additional, separately prepared component B is preferably astyrene-acrylonitrile copolymer, an α-methylstyrene-acrylonitrilecopolymer or a α-methylstyrene-styrene-acrylonitrile terpolymer. Thesecopolymers may be used for component B either as individual polymers orelse as a mixture, and therefore the additional, separately preparedcomponent B of the molding compositions used according to the inventionmay be, for example, a mixture of a styrene-acrylonitrile copolymer withan α-methylstyrene-acrylonitrile copolymer. In the event that componentB of the molding compositions used according to the invention iscomposed of a mixture of a styrene-acrylonitrile copolymer with anα-methylstyrene-acrylonitrile copolymer, the acrylonitrile contents ofthe two copolymers should preferably differ from one another by not morethan 10% by weight, preferably not more than 5% by weight, based on thetotal weight of the copolymer. Component B of the molding compositionsused according to the invention may, however, also be composed solely ofa single styrene-acrylonitrile copolymer if the starting materials forthe graft copolymerizations to prepare component A and for thepreparation of the additional, separately prepared component B are thesame monomer mixture of styrene and acrylonitrile.

The additional, separately prepared component B may be obtained by theconventional processes. In one embodiment of the invention, therefore,the copolymerization of the styrene and/or of α-methylstyrene with theacrylonitrile may be carried out in bulk, solution, suspension oraqueous emulsion. Component B preferably has a viscosity number of from40 to 100, preferably from 50 to 90, in particular from 60 to 80. Theviscosity number is determined here in accordance with DIN 53 726,dissolving 0.5 g of material in 100 ml of dimethylformamide.

Components A and B, and, if desired, C and D, may be mixed in anydesired manner using any of the known methods. If, for example,components A and B have been prepared by emulsion polymerization, thepolymer dispersions obtained may be mixed with one another, the polymersthen precipitated together and the polymer mixture worked up. However,the blending of components A and B preferably takes place by extruding,kneading or rolling the components together. If required, the componentshave previously been isolated from the aqueous dispersion or solutionobtained in the polymerization. The products of the graftcopolymerization (component A) which have been obtained in aqueousdispersion may also be only partly dewatered and mixed in the form ofmoist crumbs with component B. In this case the complete drying of thegraft copolymers takes place during the mixing.

In a preferred embodiment, the molding compositions used according tothe invention for producing the novel covering grid plates comprise,besides components A and B, additional components C and/or D, and also,if desired, other additives, as described below.

COMPONENT C

Suitable polycarbonates C are known per se. They preferably have a molarmass (weight average MW, determined using gel permeation chromatographyin tetrahydrofuran against polystyrene standards) in the range from10,000 to 60,000 g/mol. They are obtainable, for example, by theprocesses of DE-B-1 300 266 by interfacial polycondensation or by theprocess of DE-A-1 495 730 by reacting diphenyl carbonate withbisphenols. A preferred bisphenol is 2,2-di(4-hydroxyphenyl)propane,referred to generally, and also below, as bisphenol A.

Instead of bisphenol A use may also be made of other aromatic dihydroxycompounds, in particular 2,2-di(4-hydroxyphenyl)pentane,2,6-dihydroxynaphthalene, 4,4'-dihydroxydiphenyl sulfone,4,4'-dihydroxydiphenyl ether, 4,4'-dihydroxydiphenyl sulfite,4,4'-dihydroxydiphenylmethane, 1,1-di(4-hydroxyphenyl)ethane,4,4-dihydroxydiphenyl or dihydroxydiphenylcycloalkanes, preferablydihydroxydiphenylcyclohexanes or dihydroxycyclopentanes, in particular1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, or also mixtures ofthe abovementioned dihydroxy compounds.

Particularly preferred polycarbonates are those based on bisphenol A orbisphenol A together with up to 80 mol % of the abovementioned aromaticdihydroxy compounds.

It is also possible to use copolycarbonates according to U.S. Pat. No.3,737,409. Copolycarbonates based on bisphenol A anddi(3,5-dimethyldihydroxyphenyl) sulfone are of particular interest hereand have high heat resistance. It is also possible to use mixtures ofdifferent polycarbonates.

According to the invention, the average molar masses (weight average MWdetermined with the aid of gel permeation chromatography intetrahydrofuran against polystyrene standards) of the polycarbonates Care in the range from 10,000 to 64,000 g/mol. They are preferably in therange from 15,000 to 63,000 g/mol, in particular from 15,000 to 60,000g/mol. This implies that the polycarbonates C have relative solutionviscosities, measured in 0.5% strength by weight solution indichloromethane at 25° C., in the range from 1.1 to 1.3, preferably from1.15 to 1.33. The relative solution viscosities of the polycarbonatesused preferably do not differ by more than 0.05, in particular not morethan 0.04.

The polycarbonates C may be used either as ground material or aspellets. They are present as component C in amounts of from 0 to 50% byweight, preferably from 10 to 40% by weight, based in each case on theentire molding composition.

In one embodiment of the invention, the addition of polycarbonatesleads, inter alia, to higher thermal stability and improved crackingresistance of the molding compositions used according to the inventionfor producing the novel covering grid plates.

COMPONENT D

The preferred thermoplastic molding compositions used according to theinvention for producing the novel covering grid plates comprise, ascomponent D, from 0 to 50% by weight, preferably from 0 to 40% byweight, in particular from 0 to 30% by weight, of fibrous or particulatefillers or mixtures of these, based in each case on the entire moldingcomposition. These are preferably commercially available products.Reinforcing agents, such as carbon fibers and glass fibers, are usuallyused in amounts of from 5 to 50% by weight, based on the entire moldingcomposition.

The glass fibers used may be made from E, A or C glass and havepreferably been provided with a size and with a coupling agent. Theirdiameter is generally from 6 to 20 μm. Use may be made either ofcontinuous fibers (rovings) or of chopped glass fibers (staple) with alength of from 1 to 10 μm, preferably from 3 to 6 μm.

It is also possible to use fillers or reinforcing substances such asglass beads, mineral fibers, whiskers, alumina fibers, mica, powderedquartz and wollastonite.

In addition, metal flakes (e.g. aluminum flakes from Transmet Corp.),metal powders, metal fibers, metal-coated fillers, e.g. nickel-coatedglass fibers, and also other additives which screen electromagneticwaves, may be admixed with the molding compositions used according tothe invention for producing the novel covering grid plates. Aluminumflakes (K 102 from Transmet) are particularly suitable for EMI(electromagnetic interference) purposes. The compositions may also bemixed with additional carbon fibers, carbon black, in particularconductivity black, or nickel-coated carbon fibers.

The molding compositions used according to the invention for producingthe novel covering grid plates may also comprise other additives typicalof and commonly used for polycarbonates or for SAN polymers or for graftcopolymers or for mixtures of these. Examples of additives of this typeare: dyes, pigments, colorants, antistats, antioxidants, stabilizers forimproving thermal stability, for increasing photostability and forraising hydrolysis resistance and chemicals resistance, agents tocounteract thermal decomposition, and in particular the lubricants whichare useful for producing moldings. These other additives may be meteredin at any stage of the production process, but preferably at an earlyjuncture in order to make early use of the stabilizing effects (or otherspecific effects) of the additive. Heat stabilizers or oxidationinhibitors are usually metal halides (chlorides, bromides or iodides)derived from metals of group I of the Periodic Table of the Elements,for example Li, Na, K or Cu.

Suitable stabilizers are the usual hindered phenols, or else vitamin Eand/or compounds of similar structure. HALS stabilizers (hindered aminelight stabilizers), benzophenones, resorcinols, salicylates,benzotriazoles and other compounds are also suitable (for exampleIrganox®, Tinuvin®, such as Tinuvin® 770 (HALS absorber,bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate) or Tinuvin®P (UV absorber(2H-benzotriazol-2-yl)-4-methylphenol), Topanolt®). These are usuallyused in amounts of up to 2% by weight (based on the entire mixture).

Suitable lubricants and mold-release agents are stearic acids, stearylalcohol, stearates and/or higher fatty acids in general, derivatives ofthese and corresponding fatty acid mixtures having from 12 to 30 carbonatoms. The amounts of these additions are in the range from 0.05 to 1%by weight.

Other possible additives are silicone oils, oligomeric isobutylene orsimilar substances, usually in amounts of from 0.05 to 5% by weight. Itis also possible to use pigments, dyes and color brighteners, such asultramarine blue, phthalocyanines, titanium dioxide, cadmium sulfidesand derivatives of perylenetetracarboxylic acid.

Processing aids and stabilizers, such as UV stabilizers, lubricants andantistats, are usually used in amounts of from 0.01 to 5% by weight,based on the entire molding composition.

The thermoplastic molding compositions used according to the inventionfor producing the novel covering grid plates may be prepared byprocesses known per se, by mixing the components. It can be advantageousto premix individual components. It is also possible to mix thecomponents in solution and to remove the solvent.

Suitable organic solvents are, for example, chlorobenzene, mixtures ofchlorobenzene and methylene chloride or mixtures of chlorobenzene or ofaromatic hydrocarbons, e.g. toluene.

The removal of solvent from the solvent mixtures may take place, forexample, in vented extruders.

The mixing of the, for example, dry components may take place by any ofthe known methods. However, the mixing is preferably carried out byrolling, kneading or extruding the components together, preferably attemperatures of from 180 to 400° C. If necessary, the components maypreviously have been isolated from the solution obtained during thepolymerization, or from the aqueous dispersion.

The components here may be metered in either together or separately/insuccession.

In one embodiment of the invention, the novel covering grid plates andfastening parts for these may be produced by the known thermoplasticprocessing methods from the thermoplastic molding compositions usedaccording to the invention. In particular, they may be produced bythermoforming, extrusion, injection molding, calendering, blow molding,compression molding, pressure sintering or sintering, preferably byinjection molding.

The novel covering grid plates may be either in the outdoor sector(outside buildings) or in the indoor sector (within buildings). In oneembodiment of the invention, they may be colored, if desired, usingpigments or dyes.

The covering grid plates may be used to cover fans.

The novel covering grid plates may also be used to cover openings forcooling of electrical devices which are, for example, cooled using afan.

The novel covering grid plates for ventilator openings are constructedhere in such a way that they permit successful passage of air or ofother gases, but at the same time cover the opening to the extent thatpenetration by foreign bodies is avoided or made impossible and the riskof human injury is minimized.

The novel covering grid plates for ventilator openings may therefore beused in small electrical devices, such as computers or electricalmeasuring or control devices. It is possible here with the aid of themolding compositions used according to the invention to construct finestructures without the formation of visible weld lines.

In one embodiment of the invention, the covering grid plates are usedfor ventilator openings in air conditioning, in particular for airconditioning of rooms or of vehicles. The covering grid plates may beused for introducing or removing air, for example for air supply ductsor exhaust ducts.

In one embodiment of the invention, the covering grid plates are usedfor ventilator openings which are openings involving exchange of gasessolely through a temperature gradient and not by any machinery. This maybe the case, for example, for ventilator openings of electrical deviceswhich have no cooling fan.

The ventilator grids may also be used for the introduction and/orremoval of gases other than air. However, these gases must not enterinto any chemical reaction with the novel covering grid plates. Thisrisk, however, is very low due to the high chemicals resistance of thenovel covering grid plates.

The novel covering grid plates for ventilator openings may have anydesired shape which is suitable. In one embodiment of the invention,they have a circular or polygonal perimeter. The grids may have beenformed by parallel-running rods and/or fins, or, in one embodiment ofthe invention, by intersecting rods, where the angle of intersection maybe set as desired. According to the invention, the rods and/or fins mayalso run in such a way as to form a star shape. The novel covering gridplates may also have a lamella structure which guides and/or deflectsthe flow of air and/or of gas into a particular direction. The crosssection of the rods and/or fins and/or lamellae may be selected asdesired. Suitable geometries are known to the person skilled in the art.

The rods and/or fins may also be ring-shaped, connected by fins runningradially.

The novel covering grid plates for ventilator openings here have highyellowing resistance and high weathering resistance. This isparticularly important since when the covering grid plates are used incooling equipment (such as fans) the air flowing through the grid iswarm to hot. Applications of this type are therefore also dependent ongood heat resistance.

Covering grid plates made from molding compositions which comprisepolycarbonates as component C, in particular, are very heat-resistantand capable of resisting prolonged periods of heat. The addition of thepolycarbonate as component C here further improves the heat resistanceand impact strength of the covering grid plates. These covering gridplates also have a balanced ratio of toughness to stiffness and gooddimensional stability, and also excellent ability to resist heat aging,and high yellowing resistance under thermal stress and on exposure to UVradiation.

This use of the covering grid plates is another embodiment of theinvention.

Covering grid plates made from molding compositions which comprisecomponents A and B have excellent surface finishes, which are obtainedwithout further surface treatment. The appearance of the finishedsurfaces of the covering grid plates can be modified by appropriatemodification of the morphology of the rubber, for example to achievelustrous or matt surface finishes. When exposed to weathering and UVradiation, the covering grid plates show very little graying and/oryellowing, and the surface properties are therefore retained. Otheradvantageous properties of the covering grid plates are their highweathering resistance, good heat resistance, high yellowing resistancewhen exposed to UV radiation and thermal stress, good stress-crackingresistance, especially when exposed to chemicals, and goodantielectrostatic performance. They also have a high level ofcolorfastness, for example partly as a consequence of their excellentresistance to yellowing and embrittlement. The novel covering gridplates made from the thermoplastic molding compositions used accordingto the invention show no significant loss of toughness or impactstrength, either at low temperatures or after prolonged exposure toheat; these properties are retained even after exposure to UV radiation.The tensile strength is also retained. In addition, they have a balancedratio of stiffness to toughness.

According to the present invention, it is possible to reuse already usedthermoplastic molding compositions for producing the novel covering gridplates. The high colorfastness, weathering resistance and agingresistance of the molding compositions used according to the inventiongives them very good suitability for recycling. The proportion ofrecycled molding composition here can be high. For example, use of 30%by weight of previously-used molding composition, admixed in ground formwith the molding compositions used according to the invention, does notsignificantly change the relevant material properties, such asflowability, Vicat softening point and impact strength, of the moldingcompositions and of the novel covering grid plates produced therefrom.Similar results were achieved in studies of weathering resistance. Theimpact strength was also constant over a long period when reusedthermoplastic molding compositions were used, see Lindenschinidt,Ruppmich, Hoven-Nievelstein, International Body Engineering Conference,Sep. 21-23, 1993, Detroit, Mich., USA, Interior and Exterior Systems,pages 61-64. Resistance to yellowing was also retained.

The invention is described in more detail using the examples below.

EXAMPLES Example 1

Preparation of Fine-particle Graft Copolymer (A)

(a1) 16 parts of butyl acrylate and 0.4 part of tricyclodecenyl acrylatewere heated to 60° C. with stirring in 150 parts of water with additionof 1 part of the sodium salt of a C₁₂ -C₁₈ paraffin sulfonic acid, 0.3part of potassium persulfate, 0.3 part of sodium hydrogencarbonate and0.15 part of sodium pyrophosphate. 10 minutes after the polymerizationreaction had begun, a mixture of 82 parts of butyl acrylate and 1.6parts of tricyclodecenyl acrylate was added within a period of 3 hours.After monomer addition had ended, the reaction was allowed to continuefor a further hour. The resultant latex of the crosslinked butylacrylate polymer had a solids content of 40% by weight. The medianparticle size (weight average) was determined as 76 nm. The particlesize distribution was narrow (quotient Q=0.29).

(a2) 150 parts of the polybutyl acrylate latex obtained in (a1) weremixed with 40 parts of a mixture of styrene and acrylonitrile (weightratio 75:25) and 60 parts of water, and heated to 65° C. for 4 hourswith stirring after adding a further 0.03 part of potassium persulfateand 0.05 part of lauroyl peroxide. After the graft copolymerization hadended, the polymerization product was precipitated from the dispersionat 95° C. using calcium chloride solution washed with water and dried ina stream of warm air. The degree of grafting of the graft copolymer was35%.

Example 2

Preparation of Coarse-particle Graft Copolymer (A)

(a1) 50 parts of water and 0.1 part of potassium persulfate were addedto 2.5 parts of the latex prepared in step (a1) in Example 1, over thecourse of 3 hours, a mixture of 49 parts of butyl acrylate and 1 part oftricyclodecenyl acrylate and, secondly, a solution of 0.5 part of thesodium salt of a C₁₂ -C₁₈ paraffinsulfonic acid in 25 parts of waterwere run in at 60° C. After the feed had ended, polymerization wascontinued for 2 hours. The resultant latex of the crosslinked butylacrylate polymer had a solids content of 40%. The median particle size(weight average of the latex) was determined as 288 nm. The particlesize distribution was narrow (Q=0.1).

(a2) 150 parts of this latex were mixed with 40 parts of a mixture ofstyrene and acrylonitrile (ratio 75:25) and with 110 parts of water, andheated at 65° C. for 4 hours with stirring after addition of a further0.03 part of potassium persulfate and 0.05 part of lauroyl peroxide. Thepolymerization product obtained in the graft copolymerization was thenprecipitated from the dispersion at 95° C. using calcium chloridesolution, separated off, washed with water and dried in a stream of warmair. The degree of grafting of the graft copolymer was determined as27%.

Example 3

Preparation of Coarse-particle Graft Copolymer (A)

(a1) 16 parts of butyl acrylate and 0.4 part of tricyclodecenyl acrylatewere added to 150 parts of water and 0.5 part of the sodium salt of aC₁₂ -C₁₈ paraffinsulfonic acid, 0.3 part of potassium persulfate, 0.3part of sodium hydrogencarbonate and 0.15 part of sodium pyrophosphatewere run in and the mixture was heated to 60° C. with stirring. 10minutes after the polymerization reaction had begun, a mixture of 82parts of butyl acrylate and 1.6 parts of tricyclodecenyl acrylate wasadded within a period of 3 hours. After the monomer addition had ended,the reaction was allowed to continue for a further hour. The resultantlatex of the crosslinked butyl acrylate polymer had a solids content of40% by weight. The median particle size (weight average) was determinedas 216 nm. The particle size distribution was narrow (Q=0.29).

(a2) 150 parts of the polybutyl acrylate latex obtained in (a1) weremixed with 20 parts of styrene and 60 parts of water and heated at 65°C. for 3 hours with stirring after addition of a further 0.03 part ofpotassium persulfate and 0.05 part of lauroyl peroxide. After the firststep of the graft copolymerization had ended the graft copolymer had adegree of grafting of 17%. This graft copolymer dispersion, withoutfurther additives, was polymerized with 20 parts of a mixture of styreneand acrylonitrile (ratio 75:25) for a further 3 hours. After the graftcopolymerization had ended, the product was precipitated from thedispersion using calcium chloride solution at 95° C., washed with waterand dried in a stream of warm air. The degree of grafting of the graftcopolymer was 35% and the median particle size of the latex particleswas determined as 238 nm.

Example 4

Preparation of Coarse-particle Graft Copolymer (A)

(a1) 50 parts of water and 0.1 part of potassium persulfate were addedto 2.5 parts of the latex prepared in Example 3 (component A). A mixtureof 49 parts of butyl acrylate and 1 part of tricyclodecenyl acrylateand, secondly, a solution of 0.5 part of the sodium salt of a C₁₂ -C₁₈-paraffinsulfonic acid in 25 parts of water were run in at 60° C. Afterthe feed had ended, polymerization was continued for 2 hours. Theresultant latex of the crosslinked butyl acrylate polymer had a solidscontent of 40%. The median particle size (weight average) of the latexwas determined as 410 nm. The particle size distribution was narrow(Q=0.1)

(a2) 150 parts of the polybutyl acrylate latex obtained in (a1) weremixed with 20 parts of styrene and 60 parts of water and heated at 65°C. for 3 hours with stirring after addition of a further 0.03 part ofpotassium persulfate and 0.05 part of lauroyl peroxide. The dispersionobtained in this graft copolymerization was then polymerized with 20parts of a mixture of styrene and acrylonitrile in a ratio of 75:25 fora further 4 hours. The reaction product was then precipitated from thedispersion using a calcium chloride solution at 95° C., separated off,washed with water and dried in a stream of warm air. The degree ofgrafting of the graft copolymer was determined as 35% and the medianparticle size of the latex particles was 490 nm.

Example 5

Preparation of Coarse-particle Graft Copolymer (A)

(a1) 98 parts of butyl acrylate and 2 parts of tricyclodecenyl acrylatewere polymerized at 65° C. for 3 hours with stirring in 154 parts ofwater with addition of 2 parts of sodium dioctyl sulfosuccinate (70%strength) as emulsifier and 0.5 part of potassium persulfate. This gavean approximately 40% strength dispersion. The median particle size ofthe latex was about 100 nm.

2.5 parts of this latex were mixed with 400 parts of water and 0.5 partof potassium persulfate, and a mixture of 49 parts of butyl acrylate, 1part of tricyclodecenyl acrylate and 0.38 part of the emulsifier wasadded at 65° C. within a period of 1 hour. During the course of afurther hour a mixture of 49 parts of butyl acrylate, 1 part oftricyclodecenyl acrylate and 0.76 part of emulsifier was added. Afteraddition of 1 part of potassium persulfate in 40 parts of water, amixture of 196 parts of butyl acrylate, 4 parts of tricyclodecenylacrylate and 1.52 parts of the emulsifier was finally added dropwisewithin a period of 2 hours. The polymerization of the polymer mixturewas then continued for a further 2 hours at 65° C. This gave anapproximately 40% strength dispersion with an average particle diameterof about 500 nm.

If, instead of 300 parts of monomers, only 100 parts were added, thelatex obtained then had an average particle diameter of about 300 nm.

(a2) 465 parts of styrene and 200 parts of acrylonitrile werepolymerized at 60° C., with stirring, in the presence of 2500 parts ofthe polymer latex of (a1) with the median particle size of,respectively, 0.1, 0.3 and 0.5 μm, 2 parts of potassium sulfate, 1.33parts of lauroyl peroxide and 1005 parts of water. This gave a 40%strength dispersion from which the solid product was precipitated byaddition of a 0.5% strength solution of calcium chloride, washed withwater and dried.

Example 6

Preparation of Copolymer (B)

A monomer mixture of styrene and acrylonitrile was polymerized underconventional conditions in solution. The resultant styrene-acrylonitrilecopolymer had an acrylonitrile content of 35% by weight, based on thecopolymer, and a viscosity number of 80 ml/g.

Example 7

Preparation of Copolymer (B)

A monomer mixture of styrene and acrylonitrile was polymerized underconventional conditions in solution. The resultant styrene-acrylonitrilecopolymer had an acrylonitrile content of 35% by weight, based on thecopolymer, and a viscosity number of 60 ml/g.

Example 8

Preparation of Copolymer (B)

A monomer mixture of styrene and acrylonitrile was polymerized underconventional conditions in solution. The resultant styrene-acrylonitrilecopolymer had an acrylonitrile content of 27% by weight, based on thecopolymer, and a viscosity number of 80 ml/g.

Comparative Example 1

ABS Polymer

The comparative polymer used was a polybutadiene rubber which had beengrafted with a styrene-acrylonitrile copolymer as component (A), in astyrene-acrylonitrile copolymer matrix as component (B). The content ofgraft rubber was 23% by weight, based on the total weight of thefinished polymer.

Comparative Example 2

ABS Polymer

The comparative polymer used was an ABS polymer as described inComparative example 1, but with 0.5% by weight of an HALS stabilizer(Tinuvin® 770) and 0.5% by weight of a UV absorber (Tinuvin® P from CIBAG).

Comparative Example 3

HIPS Polymer

An HIPS polymer (High Impact Polystyrene: impact-modified polystyrene)was used as another molding composition for comparative purposes. It wascomposed of polystyrene with a proportion of 6.5% by weight ofpolybutadiene rubber. The damping maximum for mechanical damping is at-75° C. The MVR 200/5 was 4 m/l 10 min.

Example 9

As given in Table 1 below, the stated amounts of the appropriatepolymers (A) and (B) and, respectively, of the comparative compositionswas mixed in a screw extruder at from 200 to 230° C. The moldingcompositions formed in this way were used to produce moldings ofdiameter 60 mm and thickness 2 mm for the outdoor weatheringexperiments.

To evaluate weld line formation, dumbbell specimens were injectionmolded. The injection molding conditions here were as follows:

Polymer temperature: 250° C.

Mold temperature: 60° C.

Injection time: 1 second.

The mold used to produce the dumbbell specimens for evaluating thedevelopment of weld lines had 2 gates at the opposite faces of thedumbbell specimen which are furthest apart. When normal dumbbellspecimens are produced there is a gate only on one of these faces (inthe area of the shoulder). This design of mold means that the moldingcomposition is injected from 2 opposite sides in a longitudinaldirection into the cavity of the dumbbell mold, in such a way that thetwo streams of molding compositions meet in the middle of the mold. Insome cases a visible weld line forms at this point.

For the outdoor weathering experiments, each of the molding compositionsused was colored with, based on the total weight, 2% by weight of TiO2.

In molding compositions III and comp. II, an HALS stabilizer (Tinuvin770: bis(2,2,6,6-tetramethyl-4-piperidyl) sebacate) and a UV absorber(Tinuvin P: 2(2H-benzotriazole-2,4-methylphenol)) were used, in eachcase at 0.5% by weight. Both of these products are obtainable from CIBA.

The results of experiments are given in the table below:

                  TABLE 1                                                         ______________________________________                                                   Outdoor weathering                                                              Yellowness index                                                   as a function of Penetration                                                  insolation hours energy in                                                                                   2   Nm after                                                                              Gloss in %                         Molding Comp.   5  5 weeks after weeks                                      compo- from    P         0   10  0   ISO 6603-2  2   4                        sition Ex.     ts    0   0   00  0   0   8   12  0   0                                                     0                                                ______________________________________                                        I      A:1     4     8   7   8   1   2   3   31  1   9                                                     8                                                    2    2 8 1  0 5 5                                                                     0                                                                    B:6 5                                                                          8                                                                           II A:1 2 8 7 8 1 3 3 15 1 9 8                                                   5    2 9 0  0 3 2                                                                     0                                                                    A:3 1                                                                          0                                                                            B:6 1                                                                          0                                                                            B:7 5                                                                          5                                                                           III A:1 2 8 7 7 7 3 3 30 1 9 8                                                  5     9 0  0 4 4                                                                      0                                                                    A:3 1                                                                          0                                                                            B:6 1                                                                          0                                                                            B:7 5                                                                          5                                                                           Comp.I Comp.1  8 2 25 3 3 3 3 1 <  <                                              0  3 0   0 2 2                                                                      0 0 0                                                               Comp.II Comp.2  8 1 18 2 3 3 3 1 4 <                                              4  5 0   0 0 2                                                                      0  0                                                                Comp.III Comp.3  8 2 33 3 2 < <1 1 < <                                            5  9 0 1  0 1 1                                                                     0 0 0                                                             ______________________________________                                    

                  TABLE 1.1                                                       ______________________________________                                        Weld line                                                                       Molding                   Weld line visual                                    composition Comp. Ex. Pts. assessment on tensile specimen                   ______________________________________                                        I       A:1       42      slight weld-line visibility                            B:6 58                                                                       II A:1 25 no weld line visible                                                 A:3 10                                                                        B:6 10                                                                        B:7 55                                                                       III A:1 25 no weld line visible                                                A:3 10                                                                        B:6 10                                                                        B:7 55                                                                       Comp. I Comp. 1  slight weld-line visibility                                  Comp. II Comp. 2  slight weld-line visibility                                 Comp. III Comp. 3  marked weld-line visibility                              ______________________________________                                    

It can be seen from the results that after outdoor weathering themolding compositions according to the invention have significantly loweryellowness indices than the comparative molding compositions. Theytherefore have significantly less yellowing. At the same time, thepenetration energy is significantly higher, and this is attributable togreater strength after weathering. In addition, gloss is significantlyhigher than for the comparative compositions, and this indicates thatthe surface properties have been retained.

From the weld line experiments it can be seen that the moldingcompositions according to the invention do not give a visible weld line,or in one instance give a weld line which is just visible. The weldlines given by the comparative compositions have at least slightvisibility in every case.

It is clear from the experimental results above that the novel coveringgrid plates for ventilator openings have high yellowing resistance andhigh weathering resistance. These result in high surface quality,retained over long periods. In addition, the molding compositions havelow tendency to develop weld lines.

We claim:
 1. A covering grid plate for ventilator openings made from athermoplastic molding composition differing from ABS and comprising,based on a total of 100% by weight of amounts of components A and B,and, optionally, C and/or D,a: as component A, from 1 to 99% by weightof a particulate emulsion polymer with a glass transition temperature ofbelow 0° C. and with a median particle size of from 50 to 1000 nm, b: ascomponent B, from 1 to 99% by weight of at least one amorphous or partlycrystalline polymer, c: as component C, from 0 to 50% by weight ofpolycarbonates, and d: as component D, from 0 to 50% by weight offibrous or particulate fillers or mixtures thereof.
 2. The covering gridplate of claim 1, wherein in the molding composition component A is agraft copolymer made froma1: from 1 to 99% by weight of a particulategraft base A1 with a glass transition temperature of below 0° C., a2:from 1 to 99% by weight of a graft A2 made from the monomers, based onA2, a21: as component A21, from 40 to 100% by weight of units of avinylaromatic monomer, and a22: as component A22, up to 60% by weight ofunits of an ethylenically unsaturated monomer,where the graft A2 iscomposed of at least one graft shell, and the graft copolymer A has amedian particle size of from 50 to 1000 nm.
 3. The covering grid plateas claimed in claim 2, wherein in the molding composition theparticulate graft base A1 in the molding composition is an acrylaterubber, EP rubber, EPDM rubber or silicone rubber.
 4. The covering gridplate as claimed in claim 3, wherein in the molding compositioncomponent A1 is composed of the following monomers:a11: as componentA11, from 80 to 99.99% by weight of a C₁ -C₁₈ -alkyl acrylate, and a12:as component A 12, from 0.01 to 20% by weight of at least onepolyfunctional crosslinking monomer.
 5. The covering grid plate asclaimed in claim 1, wherein in the molding composition the particle sizedistribution of component A is bimodal, where, based on the total weightof component A, from 60 to 90% weight has a median particle size of from50 to 200 nm from 10 to 40% by weight has a median particle size of from50 to 400 nm.
 6. The covering grid plates as claimed in claim 1, whichare used in the outdoor sector.
 7. The covering grid plates as claimedin claim 1, which are used for ventilation openings in the indoorsector.
 8. The covering grid plates as claimed in claim 7, which coverfans.
 9. The covering grid plates as claimed in claim 7, which covercooling fans of electrical devices.